<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        // Dom  Document object Model  文档对象模型
        const arr = ['a', 'b', 'c']
        const str = 'hello world'

        console.log('1',!!~arr.indexOf('b'))
        console.log('2',arr.indexOf('b'))
    </script>
</body>
</html>